The Python Apprentice

Reading binary files

Now that we're producing beautiful Mandelbrot images, we should see about reading those BMPs back with Python. We're not going to write a full-blown BMP reader, although that would be an interesting exercise. We'll just make a simple function to determine the image dimension in pixels from a BMP file. We'll add the code into bmp.py:

def dimensions(filename):    """Determine the dimensions in pixels of a BMP image.    Args:        filename: The filename of a BMP file.    Returns:        A tuple containing two integers with the width        and height in pixels.    Raises:        ValueError: If the file was not a BMP file.        OSError: If there was a problem reading the file.    """    with open(filename, 'rb') as f:        magic = f.read(2)        if magic != b'BM': raise ValueError("{} ...